There are presently many uses for light sources that can change color. One popular light source is constructed from light emitting diodes (LEDs). One problem is that each LED can only emit light of a single color and usually these colors are monochromatic. Today, these colors are red, green, blue or amber. A multicolor light source could be built with combinations of LED chips (red, blue, green, amber) and then by selectively activating the chips, one of the colors could be achieved. Colors other than the individual chip color could be obtained by activating two or more different color chips at one time. This, however, will result in poor (uneven) color mixing.
Additional colors can be achieved by surrounding each LED chip with a color changing medium. For example, by using yellow phosphorus with a blue LED, the color white can be achieved. Phosphors are selected based upon their absorption and emission characteristics. Using this arrangement, a larger number of colors can be achieved, all of which fall on the border of the CIE diagram since they are all saturated colors. Saturated colors are normally produced by the diodes which emit a certain color or wavelength. If this color is not absorbed by the phosphor, a saturated color (generally) will result. Saturated colors can also be produced using the phosphor loading (max) depending on the color desired.